Manufacture of manganates



J. R. MACMILLAN, MANUFACTURE OF MANGANATES. APPLICATION FILED IUNE H. 918. 1 ,318,891 Patented Oct. 14,1919. 2 SHEET$5HEET I- l. R. MACMILLAN. MANUFACTURE OFMANGANATES.

' APPLICATION FILED JUNE 11. 1918. 1,318,891. 1 Patented 001. 14,1919. 2 SHEETS-SHEET 2. I

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JOHN R. MACMILLAN. OF NIAGARA FALLS, NEW YORK.

MANUFACTURE OF MANGANATES.

Application filed June 11,

To all whom it may concern:

Be it known that I, JOHN R. MAoMrLLAN, a citizen of the United States, residing at N'agara Falls,'in the county of Niagara and State of New York, have invented certain new and useful Improvements in the Manufacture of Manganates, of which the following is a specification.

This invention relates to the manufacture of manganates; and it comprises a method of making alkaline manganates, such as sodium manganate, wherein a mixture of manganese oxid and caustic alkali is submitted to a grinding or comminuting operation at a temperature sufficient to cause free absorption of atmospheric oxygen; all as more fully hereinafter set forth and as claimed.

In the manufacture of permanganates and manganates, it has long been the practice to heat a mixture of. manganese dioxid, MnO with a caustic alkali, usually caustic soda or caustic potash, in the presence of air or oxidizing materials. Barytes, lime, etc., are more rarely used. By a well understood re action, under these conditions some or all of the manganese dioxid takes up an additional atom of oxygen and unites with the alkali tov form a manganate, such as Na MnO Fronr this manganate apermanganate is afterward made by methods not here important. In principle the reaction is simple; but it is one diflicult to carry out on any large commercial scale, this being partly because of the corrosive and caustic properties of the alkali and partly because of the physical character of a mixture of readily fusible alkali and infusible manganese dioxid (peroxid). If air be relied on to furnish the necessary oxygen, absorption is slow at low temperatures and at higher the mixture becomes a pasty mass hardto handle. For any quick action, air must of course have free access to every portion of the mass and this is diflicult to secure. With aerial oxidation, the mixture is usuall Y heated in a reverberatory furnace with ree access of air above the hearth and is rabbled or stirred by workmen; a matter of some difficulty for the noted reasons. As usually conducted, complete oxidation of the mass requires a long time and much labor if any substantial quantity is being handled. In practice, in order to make the work easier, it is customary to use an excess of caustic soda over that Specification of Letters Patent.

PatentedOct. 14, 1919.

1918. Serial No. 239,493.

theoretically required; this excess making the mass somewhat thinner and easier to work and also accelerating the formation of 'manganate.

I have found that I can effect a rapid and complete oxidation of manganese dioxid to form sodium manganate by air at a relatively low temperature, say 400 to 550 C., by simply grinding or comminuting the mass of the mixture of dioxid and caustic soda in a hot mill in such a manner as to expose extensive and constantly changing faces to the action of air. In so doing every particle of the dioxid in the mass is positively exposed to action of the air and the attack of the air and alkali on it is much hastened.

In effect, I secure a quick action at a low temperature; a temperature at which the mechanical properties of the mass are not so inconvenient as in prior methods. It may be, indeed, with proper propo-rtioning of materials a readily disintegrating or dry mass breaking down into a powdery consistence. The grinding or comminution sought is that of the mass as a whole; not that of the manganese dioxid since I ordinarily preliminarily grind this as fine as practicable. Any convenient type of mill set in or on a suitable heating furnace and provided with means for causing passage of air in proximity to the grinding surfaces may be employed; but I find that it is best to use amill of the type of a chaser mill; a mill in which one grinding surface is afforded by a bottom plate or element over. which another grinding element travels. Such a mill may be simply set on a furnace chamber with its bottom plate forming the furnace top; or the grinding elements may be electrically heated. Any means of securing the necessary temperature at the point of grinding may be used. It is best to inclose the mill in a suitable housing to keep in dust.

In practice, using suitable apparatus, I find,

that I can secure a substantially complete oxidation of a charge in from ten minutes to an hour. The mill may or may not be continuously operating.

In a practical embodiment of the present invention, I first make a mixture of commercial fine ground manganese binoxid, or other suitable form of manganese oxid, with ordinary commercial caustic soda, flaked or ground, heat the mixture to drive off water moreover rather too pasty when hot for convenient work; The excess of soda however quickens oxidation. Ordinarily I find it better to usev about the theoretical amounts,

as in using a mixture of about equal parts of a good grade of manganese ore and caustic soda. Recovered manganese oxids may be used instead of the natural minerals. A good mixture is 100 parts of recovered oxid and 7 5 parts of caustic sOda. As stated, in lieu of caustic soda, the equivalentamount of caustic potash may be substituted. VVhatever the proportions of manganese oxid and alkali, the mixture is usually put on a plate, which may be of iron, and is heated by fire heat underneath until it dries out and becomes hot and powdery. This preliminary heating usually results in a certain amount of oxidation, thereby lessening, concomitantly, the time necessary in the next operation. The hot dry mixture is next hotground until a substantially complete conversion is obtained, this requiring a time which varies with the character of the mixture, the temperature and the grinding mill. Ordinarily I use a temperature between 400 and 550 during the comminution and oxidation; this temperature being that of the mass under treatment. It is not necessary that the whole apparatus be at this temperature; or that the temperature be uniform throughout. Through the mill casing'air is slowly drawn or assed in such a manner as to insure a su cient supply at the grinding surfaces. If the mill is of a continuously operating type, feed of raw mixture and discharge of finished manganate may be continuous; but otherwise I charge the mill and slowly grind the mixture until oxidation has gone as far as may be desired. The charge is then removed and cooled and treated in the usual manner to make commercial manganate or permanganate as the case may be.

The operation is exactly the same in making potassium manganate, barium manganate, strontium manganate, calcium ma-nga,

nate, etc., the corresponding alkali being simply substituted in equivalent amounts for the caustic soda in the examples given. Carbonates may be substituted for caustic alkali.

In the accompanying illustration I have shown, more or less diagrammatically, cersraeet tain apparatus within this invention and useful in the performance of the described process. In this showing Figure 1 is aside elevation;

Fig. 2 is a top plan view, and

Fig. 3 is an elevation taken at the right of Fig. 1.

In the drawings, the furnace consists of two heating chambers, 1 and 2, each provided with tiers of refractory material 3, advantageously in brick-like form, serving to direct the heat and flames toward the top of the chambers. .Stack 1 in communication with chamber 1 serves to produce the necessary draft and remove the waste gases. T he furnace chambers may be fired by means of oil burners (not shown) or other firing means of any usual construction. A mixture of a suitable manganese oxid and caustic alkali is preheated or dried on the plate 5 over heating chamber 1 and is delivered thence into a chaser millmounted over chamber 2. The mill as shown comprises standards 6 and 7 having a shaft 8 journaled therein with pulley wheel 9 keyed to the shaft. Driving pinion 10 attached to the shaft serves to drive the beveled gear 11 which in turn is keyed to shaft 12 having a bearing at 18 supported by a cross beam 1 1 connecting the two standards. Shaft 12 operates an enlarged extension 15 seated in the bearing 16 on the plate 17. This plate forms one of the grinding elements and is mounted over the top of the chamber 2. This extension 15 is bored at 18 to receive the horizontal shaft 19 carrying at either end roller elements 20 adapted to bear directly upon the plate 17. It may also carry stirring elements shown as chains 20 pivoted thereto, for turning and stirring the mass and pushing it into thepath of the grinding rolls. Above this plate are upwardly extending walls 21 to confine the material. justed with respect to the grinding plate by means of the nut 22 on shaft 12. The mill is advantageously inclosed by a hood '23, which has an opening 24 at one side in proximity to plate 5 of the heating chamber 1. This opening serves for the introduction of the predried mixture and for supplying air. In communication with the hood is a flue 25 leading to an exhaust fan 26. The amount of air passed over the material may be regulated by regulating the speed of this fan. Any dust resulting from the grinding operation goes forward to the exhaust means and may be recovered by any suitable fneans (not shown). Exit gases are sent away to waste or to a place of disposition through exhaust flue 27. The fan is mounted above the mill upon a standard or support which advantageously is as shown an I-beam 28 carrying bracket 29 supporting 'the fan. Pulley 30 mounted on shaft 31 in bracket 32 serves for driving the fan. I,

The rollers 20 may be ad- The operation of the apparatus is clear from the foregoing. The material is pre dried upon the plate shoveled through opening :24; on plate grinder 17 over the heating chamber 2 where it is subjected to comminut-ion and aeration. The roller elements. in addition to comminution, perform an etfective rabbling. To remove the charge of finished manganates. hood :23 may be detached or the material may be removed through door 24. 'ith the proper proportions and temperatures. no inconvenient sinterim or fusion occurs. the mass remaining "dry and easily ground throughout and the finished material is delivered as a powdery product, readily handled.

- necessary to increase the amount of manganese binoxid above the amount necessary for conversion into manganate with the soda present. in order to securea dry readily handled composition; although this may be done.

I regard as within my invention any procof mixing alkali and a manganese oxid and hot grinding the mixture at. a temperature where it will remain substantially dry l,utnevertheless will absorb atmospheric oxygen freely. ()xidants maybe incorporated in the mass but their use is not necessary. 'hcre an excess of manganese binoxid is used this may function to give oxygen acording to a well understood reaction. I find that for the present purposes a temperature of 400 to 550 at the grinding surfaces is desirable; this temperature with most. mixtures giving me a dry mass which absorbs" oxygen freely and is readily han- It is not died. The temperature away from the grinding surfaces may be considerably lower but. it is always desirable that the material 'be hot enough to prevent absorption of much and alkali in the presence .of airat a tem-.

perature sufficient for oxidation.

2. The process of making an alkali metal manganate which comprises comminuting a mixture of manganese oxid and alkali on and with the aid of a hard heated surface in the presence of air, such mixture being at a temperature at which free absorption of oxygen occurs andsuch surface being at a higher temperature.

3. The process of making an alkali metal inanganate which comprises mechanically comminuting a. mixture of manganese oxid and alkali in the presence of air and at. a temperature around 400 to 550 C.

4. The process of making sodium manganate which comprises mingling fine ground n'ainganese oxid and commercial caustic soda. drying and heating the mixture, and mechanically grinding at a temperature around 400 to 550 C. until a substantial amount of said manganese oxid is converted into sodium manganate. 4

In testimony whereof. I afiix my signature hereto.

JOHN R. MACMILLAN. 

